THE PERINEUM 



377 



of the urogenital diaphragm (anterior layer of triangular ligament). It is 

 traversed by the urethra and its surface is completely covered by the bulbo- 

 cavernosus (ejaculator urincv) muscle, which serves to eject the last drops of 

 urine or semen. The cms penis is firmly attached to the margin of the pubic 

 arch and is covered by the ischio-cavernosus (erector, penis} muscle. The two 

 crura converge anteriorly and lie side by side on the dorsum of the body of the 

 penis, where they are termed the corpora cavernosa. The bulb is continued 

 forwards as the corpus cavernosum urethrae (corpus spongiosum), which forms 

 the ventral part of the body of the penis. 



The superficial transverse perineal muscle lies in the most posterior part 

 of the superficial perineal pouch (Fig. 115). It cannot be exposed without 

 incising the fascia of Colles, and it forms an important landmark in perineal 

 surgery. 



FIG. 116. The Segmental Supply of the Skin in the Perineum. 



Superficial Perineal Nerves. (i) The posterior scrotal nerves, two 

 in number on each side, arise from the pudendal (S. 2, 3, and 4) and supply 

 the skin over the urogenital triangle and the scrotum. 



(2) The long perineal branch (long pudendal) of the posterior cutaneous 

 nerve of the thigh (S. i, 2, and 3) assists in the supply of the same areas. 



(3) The dorsal nerve of the penis arises from the pudendal (S. 2, 3, and 4) 

 and runs along the dorsum of the penis. It ends by supplying the glans. 



(4) The perforating cutaneous nerve (S. 2 and 3) supplies the skin in the 

 neighbourhood of the coccyx. 



(5) The perineal branch of S. 4 supplies the skin round the anus. 



(6) The inferior htzmorrhoidal nerve (p. 375) helps the perineal branch of 

 S. 4 to supply the skin round the anus. 



The superficial nerves of the perineum all spring from the 

 anterior rami of the sacral nerves. Pain may be referred to 



